Method and apparatus for acoustic testing of armatures

Abstract

An objective and non-destructive test of the fused tang/commutator bar joints in an armature, that can be used on every armature being manufactured on an armature manufacturing line, as well as apparatus for performing that test, are provided. The armature is immersed in an acoustic coupling medium. Acoustic pulses, preferably ultrasonic pulses, are beamed onto the joint and the reflected pulses are measured. The quality of the joint can be determined by comparing the reflected amplitude to the known reflected amplitudes for joints of known quality. A testing station on an armature production line includes a mechanism for removing the armature from the production line, immersing it in the coupling medium, and rotating it as each joint in the commutator of that armature is checked.

What is claimed is: 
     
       1. A method for testing the quality of a fused joint between a commutator tang and a commutator bar in a commutator of an armature of a dynamoelectric machine, said commutator bar having first and second opposed substantially parallel commutator bar surfaces, said tang having first and second opposed substantially parallel tang surfaces, said fused joint being formed between said first commutator bar surface and said first tang surface without melting any of said surfaces, said method comprising: directing an acoustic beam comprising at least one acoustic pulse toward a portion of said second tang surface along an axis substantially perpendicular to said portion of said second tang surface, at least a portion of each said at least one pulse passing through said tang and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at said joint;   measuring said reflected portion of each of said at least one pulse to determine a reflected amplitude of each of said at least one pulse; and   analyzing said measured reflected amplitude to derive an indication of the quality of said joint, said quality of said joint being representative of the quantity and size of said gaps.   
     
     
       2. The method of claim 1 wherein said analyzing step comprises: comparing said reflected amplitude to a threshold amplitude; and   characterizing said joint as unacceptable if said reflected amplitude exceeds said threshold amplitude.   
     
     
       3. The method of claim 2 further comprising the steps of: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       4. The method of claim 1 wherein said step at directing an acoustic beam along said axis comprises directing an ultrasonic beam along said axis. 
     
     
       5. The method of claim 1 wherein said directing step comprises directing said beam toward said second tang surface through a medium having a greater acoustic conductivity than air. 
     
     
       6. The method of claim 5 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium. 
     
     
       7. The method of claim 6 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium that is substantially electrically nonconductive. 
     
     
       8. The method of claim 6 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium that is substantially non-oxidizing. 
     
     
       9. Apparatus for testing the quality of a fused joint between a commutator tang and a commutator bar in a commutator of an armature of a dynamoelectric machine, said commutator bar having first and second opposed substantially parallel commutator bar surfaces, said tang having first and second opposed substantially parallel tang surfaces, said fused joint being formed between said first commutator bar surface and said first tang surface without melting any of said surfaces, said apparatus comprising: an acoustic beam emitter for directing an acoustic beam comprising at least one pulse toward a portion of said second tang surface along an axis substantially perpendicular to said portion of said second tang surface, at least a portion of each said pulse passing through said tang and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at said joint;   an acoustic receiver for measuring said reflected portion of each of said at least one pulse to determine a reflected amplitude of each of said at least one pulse; and   an analysis unit for deriving from said reflected amplitude an indication of the quality of said joint, said quality of said joint being representative of the quantity and size of said gaps.   
     
     
       10. The apparatus of claim 9 wherein said analysis unit compares said reflected amplitude to a threshold amplitude, and characterizes said joint as unacceptable if said reflected amplitude exceeds said threshold amplitude. 
     
     
       11. The apparatus of claim 10 wherein said threshold amplitude is calibrated by: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       12. The apparatus of claim 9 wherein said acoustic beam emitter is an ultrasonic beam emitter. 
     
     
       13. The apparatus of claim 9 further comprising a vessel containing a medium having a greater acoustic conductivity than air; wherein: said joint, said emitter and said receiver are immersed in said medium.   
     
     
       14. The apparatus of claim 13 wherein said medium is a liquid. 
     
     
       15. The apparatus of claim 14 wherein said liquid medium is substantially electrically nonconductive. 
     
     
       16. The apparatus of claim 14 wherein said liquid medium is substantially non-oxidizing. 
     
     
       17. The apparatus of claim 9 wherein said acoustic beam emitter and said acoustic receiver are combined in an acoustic probe. 
     
     
       18. In a manufacturing line for dynamoelectric machine armatures, an armature testing station for testing the quality of a fused joint between a commutator tang and a commutator bar in a commutator of an armature, said commutator bar having first and second opposed substantially parallel commutator bar surfaces, said tang having first and second opposed substantially parallel tang surfaces, said fused joint being formed between said first commutator bar surface and said first tang surface without melting any of said surfaces, said armature testing station comprising: an acoustic beam emitter for directing an acoustic beam comprising at least one acoustic pulse toward a portion of said second tang surface along an axis substantially perpendicular to said portion of said second tang surface, at least a portion of said at least one pulse passing through said tang and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at said joint;   an acoustic receiver for measuring said reflected portion of each of said at least one pulse to determine a reflected amplitude of said pulse; and   an analysis unit for deriving from said reflected amplitude an indication of the quality of said joint, said quality of said joint being representative of the quantity and size of said gaps.   
     
     
       19. The apparatus of claim 18 wherein said analysis unit compares said reflected amplitude to a threshold amplitude, and characterizes said joint as unacceptable if said reflected amplitude exceeds said threshold amplitude. 
     
     
       20. The armature testing station of claim 19 wherein said threshold amplitude is calibrated by: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       21. The armature testing station of claim 18 wherein said acoustic beam emitter is an ultrasonic beam emitter. 
     
     
       22. The armature testing station of claim 18 further comprising a vessel containing a medium having a greater acoustic conductivity than air; wherein: said joint, said emitter and said receiver are immersed in said medium.   
     
     
       23. The armature testing station of claim 22 wherein said medium is a liquid. 
     
     
       24. The armature testing station of claim 23 wherein said liquid medium is substantially electrically nonconductive. 
     
     
       25. The armature testing station of claim 23 wherein said liquid medium is substantially non-oxidizing. 
     
     
       26. The armature testing station of claim 22 further comprising a gripper for removing said armature from said production line, immersing said armature in said vessel for testing, and returning said armature to said production line after testing. 
     
     
       27. The armature testing station of claim 26 wherein said gripper is rotatable to allow successive testing of each of a plurality of joints of an armature. 
     
     
       28. The armature testing station of claim 18 further comprising a gripper for removing said armature from said production line, placing said armature in a location exposed to said emitter and receiver for testing, and returning said armature to said production line after testing. 
     
     
       29. The armature testing station of claim 28 wherein said gripper is rotatable to allow successive testing of each of a plurality of joints of an armature. 
     
     
       30. The armature testing station of claim 18 wherein said acoustic beam emitter and said acoustic receiver are combined in an acoustic probe. 
     
     
       31. A method for testing the quality of a plurality of fused joints of a commutator of an armature of a dynamoelectric machine in succession, each of said fused joints being between a commutator tang and a commutator bar of said commutator, said armature having a longitudinal axis and being gripped by a gripper, said joints being disposed circumferentially around said longitudinal axis of said armature, each of said commutator bars having first and second opposed substantially parallel commutator bar surfaces, each of said tangs having first and second opposed substantially parallel tang surfaces, each of said fused joints being formed between each of said first commutator bar surfaces and each of said first tang surfaces without melting any of said surfaces, said method comprising: directing an acoustic beam comprising a plurality of pulses from said emitter substantially perpendicular to and substantially toward said longitudinal axis of said armature, at least a portion of one of said plurality of pulses passing through one of said second tang surfaces and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at one of said joints;   rotating said armature around said longitudinal axis of said armature;   measuring said reflected portion of said pulse for each of said joints during said rotating to determine a reflected amplitude profile, said profile having a plurality of maxima;   correlating each of said profile maxima with each of said fused joints;   comparing each of said profile maxima with a predetermined threshold amplitude;   characterizing each of said correlated joints as unacceptable if said correlated profile maximum exceeds said threshold amplitude.   
     
     
       32. The method of claim 31 further comprising the steps of: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       33. The method of claim 31 wherein said step at directing an acoustic beam comprises directing an ultrasonic beam. 
     
     
       34. The method of claim 31 wherein said directing step comprises directing said beam toward said longitudinal axis of said armature through a medium having a greater acoustic conductivity than air. 
     
     
       35. The method of claim 34 wherein said directing step comprises directing said beam toward said longitudinal axis of said armature through a liquid medium. 
     
     
       36. The method of claim 35 wherein said directing step comprises directing said beam toward said longitudinal axis of said armature through a liquid medium that is substantially electrically nonconductive. 
     
     
       37. The method of claim 36 wherein said directing step comprises directing said beam toward said longitudinal axis of said armature through a liquid medium that is substantially non-oxidizing. 
     
     
       38. Apparatus for testing the quality of a plurality of fused joints of a commutator of an armature of a dynamoelectric machine in succession, each of said fused joints being between a commutator tang and a commutator bar of said commutator, said armature having a longitudinal axis, said joints being disposed circumferentially around said longitudinal axis of said armature, each of said commutator bars having first and second opposed substantially parallel commutator bar surfaces, each of said tangs having first and second opposed substantially parallel tang surfaces, each of said fused joints being formed between each of said first commutator bar surfaces and each of said first tang surfaces without melting any of said surfaces, said apparatus comprising: an acoustic beam emitter for directing an acoustic beam comprising a plurality of pulses from said emitter substantially perpendicular to and substantially toward said longitudinal axis of said armature, at least a portion of one of said pulses passing through one of said second tang surfaces and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at one of said joints;   a gripper for gripping said armature and for rotating said armature around said longitudinal axis of said armature;   an acoustic receiver for measuring said reflected portion of said pulse for each of said joints during said rotating to determine a reflected amplitude profile, said profile having a plurality of maxima;   an analysis unit for correlating each of said profile maxima with each of said fused joints, comparing each of said profile maxima with a predetermined threshold amplitude, and characterizing each of said correlated joints as unacceptable if said correlated profile maximum exceeds said threshold amplitude.   
     
     
       39. The apparatus of claim 38 wherein said threshold amplitude is determined by: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       40. The apparatus of claim 38 wherein said acoustic beam emitter is an ultrasonic beam emitter. 
     
     
       41. The apparatus of claim 38 further comprising a vessel containing a medium having a greater acoustic conductivity than air; wherein: said joint, said emitter and said receiver are immersed in said medium.   
     
     
       42. The apparatus of claim 40 wherein said medium is a liquid. 
     
     
       43. The apparatus of claim 42 wherein said liquid medium is substantially electrically nonconductive. 
     
     
       44. The apparatus of claim 42 wherein said liquid medium is substantially non-oxidizing. 
     
     
       45. The apparatus of claim 38 wherein said acoustic beam emitter and said acoustic receiver are combined in an acoustic probe. 
     
     
       46. A method for testing the quality of a fused joint between a commutator tang and a commutator bar in a commutator of an armature of a dynamoelectric machine, said commutator bar having first and second opposed substantially parallel commutator bar surfaces, said tang having first and second opposed substantially parallel tang surfaces, said fused joint being formed between said first commutator bar surface and said first tang surface without melting any of said surfaces, said method comprising: directing an acoustic beam comprising at least one pulse having a frequency of about 20 MegaHertz toward said second tang surface along an axis substantially perpendicular to said second tang surface, at least a portion of said pulse passing through said tang and reflecting off one or more gaps formed during fusing, said gaps being between said first commutator bar surface and said first tang surface at said joint;   measuring said reflected portion of said pulse to determine a reflected amplitude;   comparing said reflected amplitude to a predetermined threshold amplitude; and   characterizing said joint as having at least one gap having a depth greater than about 0.005 mm in a direction perpendicular to the plane of the joint if said reflected amplitude exceeds said threshold amplitude.   
     
     
       47. The method of claim 46 further comprising the steps of: determining a minimum reflected amplitude by measuring said reflected amplitude for a joint known to be of maximum quality;   determining a maximum reflected amplitude by measuring said reflected amplitude for a joint known to be of minimum quality; and   selecting said threshold amplitude, between said minimum reflected amplitude and said maximum reflected amplitude, to correspond to a desired quality between said minimum quality and said maximum quality.   
     
     
       48. The method of claim 46 wherein said step at directing an acoustic beam along said axis comprises directing an ultrasonic beam along said axis. 
     
     
       49. The method of claim 46 wherein said directing step comprises directing said beam toward said second tang surface through a medium having a greater acoustic conductivity than air. 
     
     
       50. The method of claim 49 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium. 
     
     
       51. The method of claim 50 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium that is substantially electrically nonconductive. 
     
     
       52. The method of claim 51 wherein said directing step comprises directing said beam toward said second tang surface through a liquid medium that is substantially non-oxidizing.